1. Field of Invention
The invention concerns apparatus for generating clamping force in injection molding machines, and more particularly apparatus wherein the clamping force is generated by magnetostrictive elements in the clamping mechanism.
2. Description of the Related Art
During the injection molding of thermoplastic parts, the plastic melt is injected under high pressure into the mold cavity of the injection molding die. The clamping force applied to the die must be adequate to maintain proper closure. Specifically, this clamping force or mold locking force must be greater than the expansion force that develops in the mold cavity during the injection process.
The clamping mechanisms used for injection molding are typically operated fully hydraulically, hydraulically-mechanically or electro-mechanically. For all machine types, it is necessary to configure the machine so that the clamp mechanism will produce sufficient force for securely clamping the mold elements against the injection pressure after the mold is closed.
The moving platen in hydraulic clamp mechanisms is typically moved toward the stationary platen by means of high-speed hydraulic cylinders until the mold is closed. During injection these cylinders must also create the necessary clamping pressure which naturally requires a large volume of hydraulic oil. Given the potential for leakage, the presence of oil is a real disadvantage from the standpoint of environmental protection. Moreover, there is a hazard that the hydraulic components will fail right at the point of injection, thereby posing a threat to operating personnel, not to mention the fact that unusable parts are produced.
Alternatively, the clamp mechanism can include a toggle linkage. During buildup of the clamping force the toggle-linkage bearings are subject to a high dynamic load, which enables rapid closure. In clamp mechanisms driven by an electric motor, for example, mechanisms including ball screws or trapezoidal screw threads, an enormous motor load occurs in the injection phase in order to maintain the required clamping force.
Although these various clamp mechanisms all provide two distinct functions, i.e. (1) rapid closing and opening movement at limited force, and (2) generating a large force with limited movement, both are produced by the same machine elements. Accordingly, the clamping mechanisms must be designed reliably at a reasonable cost.